1. Field of the Invention
The present invention relates to film formation using an organic silane type source gas. More specifically, the invention relates to a manufacturing method of a semiconductor device including formation of a film containing hydrogen and nitrogen which film is low in the content of carbon components and superior both in step coverage and impurity blocking performance.
2. Description of the Related Art
In LSIs, which constitute one technical field of semiconductor devices, the wiring interval is now as small as 0.2-0.4 xcexcm and the aspect ratio (height to width) of wiring lines (interconnections) now exceeds unity. To prevent voids from occurring in planarizing an interlayer insulating film, a film forming method comes to be used which utilizes superior step coverage of a film that is formed by using an organic silane type source gas such as ethyl orthosilicate (Si(OC2H5)4, what is called xe2x80x9cTEOSxe2x80x9d). In another field of liquid crystal displays in which a number of thin-film transistors are formed on an insulative substrate, the frequency of occurrence of what is called a xe2x80x9cbreak at a stepxe2x80x9d of wiring lines of thin-film transistors is lowered by utilizing superior step coverage of a film formed by using ethyl orthosilicate as a source gas. In particular, in liquid crystal displays using a process of lower than 600xc2x0 C. in contrast to high-temperature processes for silicon wafers, an ethyl orthosilicate source gas is used to form a gate oxide film and an undercoat film in addition to an interlayer insulating film.
In the field of LSIs, although an oxide film formed by using ethyl orthosilicate is used as an interlayer insulating film, it contains many carbon-hydrogen bonds and oxygen-hydrogen bonds and therefore is high in hygroscopicity. On the other hand, although a silicon nitride film exhibits high water resistance and impurity blocking performance, it is inferior in step coverage and is easily broken because of its high degree of hardness.
In thin-film transistors (TFTs), which are applied to, for instance, a liquid crystal display, an undercoat film, a gate insulating film, an interlayer insulating film, and the like are formed on an insulative substrate such as a glass substrate by thermal CVD, plasma CVD, or a like method by using an organic silane type source gas such as ethyl orthosilicate. However, having a large amount of carbon, such films are not sufficient in terms of water resistance and impurity blocking performance.
In a conventional, commonly employed film forming method that is a plasma CVD method using ethyl orthosilicate, a subject substrate is placed in a chamber having parallel-plate electrodes and capable of being evacuated. On of the electrodes is connected to a high-frequency power supply, that is, serves as the cathode. The other electrode is connected to the ground, that is, serves as the anode. The subject substrate is placed on the ground-side, i.e., anode-side electrode. Since ethyl orthosilicate assumes liquid form in the ordinary temperature, it is introduced into the chamber in a state that it is heated to increase its vapor pressure or it is introduced into the chamber together with a carrier gas by bubbling ethyl orthosilicate in a tank with the carrier gas. Ethyl orthosilicate has a feature that when decomposed in plasma, it forms precursors and flows on the substrate, thus enabling formation of a film that is superior is step coverage. Precursors moving on the substrate collide with each other, and oxygen ions, oxygen radicals, ozone molecules formed in the plasma collide with those precursors, causing abstraction reaction on the surface and thereby forming SiOx. If a larger amount of oxygen is introduced, the surface abstraction reaction due to the precursors that are formed from ethyl orthosilicate is accelerated. In this case, the step coverage is degraded though the carbon content is reduced.
On the other hand, if a smaller amount of oxygen is introduced, although the step coverage is improved, more carbon-hydrogen and oxygen-hydrogen bonds remain in the film, making it highly hygroscopic. If an infrared measurement is conducted, the absorption in the vicinity of 3,660 cmxe2x88x921 will increase with the lapse of time. The absorption at 3,660 cmxe2x88x921 is mainly due to Sixe2x80x94OH bonds and indicates that a film formed is hygroscopic.
Another film forming method using ethyl orthosilicate is an atmospheric pressure CVD method utilizing ozone and heat. In this method, a substrate is heated to 300-400xc2x0 C. An organic silane type source gas such as ethyl orthosilicate is introduced into a reaction chamber by bubbling it in a tank with N2. Ozone is also introduced into the chamber by generating it by passing oxygen through an ozonizer. Because of superior step coverage and a high film forming rate of this method, this method is used to form an interlayer insulating film for devices that include multi-layer wiring, such as LSIs and DRAMs memories. After the film formation, planarization is performed by etching back, SOG (spin on glass), CMP (chemical mechanical polishing), etc. in combination.
However, according to the above atmospheric pressure CVD method, a resulting film is very low in density, that is, a porous film is formed. Therefore, if such a film is used singly, it exhibits very high hygroscopicity, possibly causing leak between wiring lines, thus lowering the reliability of a semiconductor device. Further, at the present time when the application of the 0.3-xcexcm rules is pressing, the lateral capacitance between wiring lines is not negligible, which requires a film having a small permittivity.
Japanese Unexamined Patent Publication No. Hei. 1-48425 of the present assignee discloses a film forming method that uses an organic silane type source gas and nitrogen oxide. As disclosed in the above publication, this method can form a uniform coating on an uneven surface which coating blocks alkaline impurities. Although this coating functions satisfactorily when used only as an interlayer insulating film, the carbon content in the organic silane type source gas needs to be minimized when this coating serves as an insulating film whose electrical characteristics are important, such as a gate insulating film or a part of a capacitor. The coating cannot be used as an insulating film whose electrical characteristics are utilized unless the carbon content is controlled.
Conventionally, where a film is formed by using an organic silane type source gas such as ethyl orthosilicate, improving the step coverage necessarily causes increase in hygroscopicity and carbon content, which in turn causes reduction in reliability and degradation in semiconductor characteristics. If a large amount of oxygen is added to an organic silane type gas such as ethyl orthosilicate to decrease the carbon content, the step coverage is degraded and therefore voids, a break of a wiring line, etc. may occur, which also cause reduction in reliability and degradation in semiconductor characteristics. In addition, an oxide film is more likely contaminated by impurities such as alkali metals. Once introduced, impurities behave as operative ions (movable ions) in some cases.
An object of the present invention is to enable formation of a film which is superior in step coverage, lower in carbon content than conventional films, low in hygroscopicity, and superior in impurity blocking performance.
Another object of the invention is to enable formation of a film which is superior in step coverage, lower in carbon content than conventional films, and low in hygroscopicity, with an increased film forming rate.
To attain the above objects, according to one aspect of the invention, there is provided a manufacturing method of a semiconductor device having a step of forming an oxide film on a heated substrate by plasma CVD or atmospheric pressure CVD by using gases including an organic silane type source gas and oxygen or a source gas including ozone that is generated from oxygen, wherein:
the oxide film is formed by adding hydrogen during formation thereof, and then converting said hydrogen into hydrogen radicals; or
the oxide film is formed by converting hydrogen into hydrogen radicals, and adding the hydrogen radicals during formation of the oxide film.
According to another aspect of the invention, there is provided a manufacturing method of a semiconductor device having a step of forming an oxide film on a heated substrate by plasma CVD or atmospheric pressure CVD by using gases including an organic silane type source gas and oxygen or a source gas including ozone that is generated from oxygen, wherein:
the oxide film is formed by adding H2O during formation thereof, and then generating hydrogen radicals from said H2O.
According to another aspect of the invention, there is provided a manufacturing method of a semiconductor device having a step of forming an oxide film on at least part of a hydrophilic surface of a heated substrate by atmospheric pressure CVD by using gases including an organic silane type source gas and oxygen or a source gas including ozone that is generated from oxygen with an ozone density set at more than 1%, wherein:
the oxide film is formed by adding hydrogen during formation thereof, and then converting said hydrogen into hydrogen radicals; or
the oxide film is formed by converting hydrogen into hydrogen radicals, and adding the hydrogen radicals during formation of the oxide film.
According to another aspect of the invention, there is provided a manufacturing method of a semiconductor device having a step of forming an oxide film on a heated substrate by plasma CVD by using gases including an organic silane type source gas and oxygen or a source gas including ozone that is generated from oxygen, wherein:
an amount of said oxygen is less than 15 times an amount of the organic silane type source gas; and
the oxide film is formed by adding hydrogen at an amount not less than 0.01 times the amount of the organic silane type source gas during formation thereof, and then converting said hydrogen into hydrogen radicals.
According to another aspect of the invention, there is provided a manufacturing method of a semiconductor device having a step of forming an oxide film on a heated substrate by plasma CVD by using gases including an organic silane type source gas and oxygen or a source gas including ozone that is generated from oxygen, wherein:
an amount of said oxygen is less than 15 times an amount of the organic silane type source gas; and
the oxide film is formed by adding H2O by bubbling H2O with a carrier gas of an amount 0.1 to 1 times the amount of the organic silane type source gas during formation of the oxide film, and then generating hydrogen radicals from said H2O.
According to another aspect of the invention, there is provided a manufacturing method of a semiconductor device having a step of forming an oxide film on a heated substrate by atmospheric pressure CVD by using gases including an organic silane type source gas and oxygen or a source gas including ozone that is generated from oxygen, wherein:
the oxide film is formed by adding hydrogen at an amount not less than 0.1 times the amount of the organic silane type source gas during formation thereof, and then converting said hydrogen into hydrogen radicals.
According to another aspect of the invention, there is provided a manufacturing method of a semiconductor device having a step of forming an oxide film on a heated glass substrate by plasma CVD or atmospheric pressure CVD by using gases including an organic silane type source gas and oxygen or a source gas including ozone that is generated from oxygen under a semiconductor layer to become an active layer in a process of forming a thin-film transistor on the glass substrate, wherein:
the oxide film is formed by adding hydrogen during formation thereof, and then converting said hydrogen into hydrogen radicals; or
the oxide film is formed by converting hydrogen into hydrogen radicals, and adding the hydrogen radicals during formation of the oxide film.
According to another aspect of the invention, there is provided a manufacturing method of a semiconductor device having a step of forming an oxide film on a heated glass substrate by plasma CVD by using gases including an organic silane type source gas and oxygen or a source gas including ozone that is generated from oxygen over a semiconductor layer to become an active layer in a process of forming a thin-film transistor on the glass substrate, wherein:
the oxide film is formed by adding hydrogen during formation thereof, and then converting said hydrogen into hydrogen radicals; or
the oxide film is formed by converting hydrogen into hydrogen radicals, and adding the hydrogen radicals during formation of the oxide film.
According to another aspect of the invention, there is provided a manufacturing method of a semiconductor device having a step of forming an oxide film on a heated glass substrate by plasma CVD or atmospheric pressure CVD by using gases including an organic silane type source gas and oxygen or a source gas including ozone that is generated from oxygen over a gate insulating film in a process of forming a thin-film transistor on the glass substrate, wherein:
the oxide film is formed by adding hydrogen during formation thereof, and then converting said hydrogen into hydrogen radicals; or
the oxide film is formed by converting hydrogen into hydrogen radicals, and adding the hydrogen radicals during formation of the oxide film.
According to still another aspect of the invention, there is provided a plasma CVD apparatus for manufacture of a semiconductor device, comprising:
a vacuum chamber;
parallel plate electrodes;
a plasma power source connected to a first one of the electrodes via a matching device;
a substrate holder capable of being heated, for placing a substrate having a film forming surface on a second one of the electrodes; and
a pump connected to the vacuum chamber via a flow control valve,
wherein an organic silane type source gas and oxygen or oxygen partially converted into ozone are introduced into the vacuum chamber via respective flow rate controllers through the first electrode; and
H2O is introduced into the vacuum chamber together with a carrier gas independently of the organic silane type source gas by bubbling water in a tank with the carrier gas that is supplied via a flow rate controller.
According to another aspect of the invention, there is provided an atmospheric pressure CVD apparatus for manufacture of a semiconductor device, comprising:
a substrate holder capable of being heated, for mounting a substrate having a film forming surface; and
a gas nozzle so disposed as to be opposed to the film forming surface of the substrate,
wherein an organic silane type source gas and a carrier gas are supplied to the gas nozzle via a flow rate controller;
oxygen is supplied, via a flow rate controller, to an ozonizer for converting part of said oxygen into ozone, and then supplied to the gas nozzle; and
hydrogen is supplied, via a flow rate controller, to a catalyst for converting part of said hydrogen into hydrogen radicals, and then supplied to the gas nozzle.
To attain the above objects, according to a further aspect of the invention, there is provided a manufacturing method of a semiconductor device having a step of forming an oxide film on a heated substrate by plasma CVD or atmospheric pressure CVD by using material gases including an organic silane type source gas and hydrogen or active hydrogen, wherein:
the oxide film is formed by adding nitrogen oxide expressed as NxOy during formation thereof.
According to another aspect of the invention, there is provided a manufacturing method of a semiconductor device having a step of forming an oxide film on a heated substrate by plasma CVD or atmospheric pressure CVD by using material gases including an organic silane type source gas and H2O, wherein:
the oxide film is formed by adding nitrogen oxide expressed as NxOy during formation thereof.
According to another aspect of the invention, there is provided a manufacturing method of a semiconductor device having a step of forming an oxide film on at least part of a hydrophilic surface of a heated substrate by atmospheric pressure CVD by using material gases including an organic silane type source gas, oxygen or a source gas including ozone that is generated from oxygen, and hydrogen or active hydrogen with an ozone density set at more than 1%, wherein:
the oxide film is formed by adding nitrogen oxide expressed as NxOy during formation thereof.
According to another aspect of the invention, there is provided a manufacturing method of a semiconductor device having a step of forming an oxide film on a heated substrate by plasma CVD by using material gases including an organic silane type source gas, oxygen or a source gas including ozone that is generated from oxygen, and hydrogen or active hydrogen, wherein:
an amount of said oxygen or the source gas including ozone generated from oxygen is less than 15 times an amount of the organic silane type source gas; and
said hydrogen or active hydrogen is added at an amount not less than 0.01 times the amount of the organic silane type source gas; and
the oxide film is formed by adding nitrogen oxide expressed as NxOy during formation thereof.
According to another aspect of the invention, there is provided a manufacturing method of a semiconductor device having a step of forming an oxide film on a heated substrate by plasma CVD by using material gases including an organic silane type source gas, oxygen or a source gas including ozone that is generated from oxygen, and H2O, wherein:
an amount of said oxygen or the source gas including ozone generated from oxygen is less than 15 times an amount of the organic silane type source gas; and
said H2O is added by bubbling H2O with a carrier gas of an amount 0.1 to 1 times the amount of the organic silane type source gas during formation of the oxide film; and
the oxide film is formed by adding nitrogen oxide expressed as NxOy during formation thereof.
According to another aspect of the invention, there is provided a manufacturing method of a semiconductor device having a step of forming an oxide film on a heated substrate by atmospheric pressure CVD by using material gases including an organic silane type source gas and hydrogen or active hydrogen, wherein:
said hydrogen or active hydrogen is added at an amount not less than 0.1 times the amount of the organic silane type source gas; and
the oxide film is formed by adding nitrogen oxide expressed as NxOy during formation thereof.
According to another aspect of the invention, there is provided a manufacturing method of a semiconductor device having a step of forming an oxide film on a heated glass substrate by plasma CVD or atmospheric pressure CVD by using gases including an organic silane type source gas and hydrogen or active hydrogen under a semiconductor layer to become an active layer in a process of forming a thin-film transistor on the glass substrate, wherein:
the oxide film is formed by adding nitrogen oxide expressed as NxOy during formation thereof.
According to another aspect of the invention, there is provided a manufacturing method of a semiconductor device having a step of forming an oxide film on a heated glass substrate by plasma CVD by using gases including an organic silane type source gas and hydrogen or active hydrogen over a semiconductor layer to become an active layer in a process of forming a thin-film transistor on the glass substrate, wherein:
the oxide film is formed by adding nitrogen oxide expressed as NxOy during formation thereof.
According to another aspect of the invention, there is provided a manufacturing method of a semiconductor device having a step of forming an oxide film on a heated glass substrate by plasma CVD or atmospheric pressure CVD by using gases including an organic silane type source gas and hydrogen or active hydrogen over a gate insulating film in a process of forming a thin-film transistor on the glass substrate, wherein:
the oxide film is formed by adding nitrogen oxide expressed as NxOy during formation thereof.
According to another aspect of the invention, in the above manufacturing methods of a semiconductor device, the organic silane type source gas is one of TEOS, OMCTS, and HMDS.
According to another aspect of the invention, in the above manufacturing methods of a semiconductor device, the organic silane type source gas is a material including fluorine.
According to another aspect of the invention, in the above manufacturing methods of a semiconductor device, the nitrogen oxide expressed as NxOy is one selected from the group consisting of N2O, NO, N2O3, NO2, N2O4, N2O5, NO3 and N2O6.
According to another aspect of the invention, in the above manufacturing methods of a semiconductor device, a content of carbon expressed as C of the oxide film as measured by SIMS has a minimum value of less than 3xc3x971019 cmxe2x88x923 in a depth-direction profile, and a content of nitrogen expressed as N of the oxide film as measured by SIMS has a maximum value of more than 1xc3x971019 cmxe2x88x923 in a depth-direction profile.
The present assignee previously used a mixture of oxygen and ethyl orthosilicate in forming an oxide film by plasma CVD by using ethyl orthosilicate. As a result of various experiments to find a proper method for reducing the carbon content of a film formed, the inventors have found that it is effective to use hydrogen radicals, hydrogen ions, etc. during the film formation. Active hydrogen such as hydrogen radicals and hydrogen ions gasify carbon by reacting with it and forming CHx. It is possible to eliminate carbon during film formation particularly by cutting carbon single bonds Cxe2x80x94C to produce CH4 and Cxe2x80x94OH.
Hydrogen has a stronger decarbonization effect than oxygen. Further, since the hydrogen atom is small, the sputtering effect of hydrogen ions on a film and a substrate is almost negligible. Therefore, in forming a film by plasma CVD by mixing an organic silane type source gas, nitrogen oxide, and hydrogen, the mixing ratio of the organic silane type source gas and nitrogen oxide is so determined as to provide a film forming rate that enables superior step coverage and high productivity and hydrogen is mixed for decarbonization. In particular, the above effects are remarkable when hydrogen is introduced by an amount 0.1 to 1 times the amount of the organic silane type source gas. Plasma-generated precursors from the organic silane source gas, oxygen ions, ozone, and oxygen radicals repeat film forming surface reaction on the substrate surface. In this operation, the precursors flow above the substrate surface while transforming into various type of precursors, to form an oxide film having superior step coverage. While the oxide film is formed by reaction among the precursors, oxygen ions, ozone, and oxygen radicals, hydrogen ions and hydrogen radicals gasify carbon by reacting with carbon atoms on the substrate surface. Gasified carbon is exhausted by a vacuum pump.
If it is possible to dope an oxide film with nitrogen at the same time as reduce carbon contained therein, the advantages of both of an oxide film and a nitride film can be obtained. In particular, in forming a nitrogen-doped oxide film by using an organic silane type source gas such as ethyl orthosilicate, both oxygen and nitrogen can be supplied to a film during film formation by using nitrogen oxide (NxOy, compound of nitrogen and oxygen) such as N2O, NO, N2O3, NO2, N2O4, N2O5, NO3 and N2O6. A nitrogen-doped oxide film is much superior in water resistance and impurity blocking performance to a non-doped oxide film. In particular, alkali metals such as Na and K become operative ions moving through an oxide film, which is a major cause of unstable electrical properties of a semiconductor. A nitrogen-doped oxide film is given much improved blocking performance compared to a non-doped oxide film, and therefore can suppress the operability of alkali metals such as Na and K.
The characteristics of a nitrogen-doped oxide film can be varied by properly selecting the molecular weight of nitrogen oxide in accordance the intended characteristics and adding oxygen when it is insufficient.
Since nitrogen oxide consists of nitrogen and oxygen that are combined in advance, an oxide film formed is easily combined, i.e., doped with nitrogen when nitrogen oxide reacts with an organic silane type source gas. A nitrogen-doped oxide film can be formed by using ammonia or a mixture of nitrogen and oxygen instead of nitrogen oxide. However, since relatively large energy is needed to decompose ammonia, the film forming surface of a substrate may be seriously damaged in a plasma method or the like. Further, since nitrogen is hardly combined with other molecules, it is difficult to control the dope amount. Thus, it is very effective to use nitrogen oxide to dope an oxide film with nitrogen when it is formed by using an organic silane type source gas.
Where the invention is applied to film formation by atmospheric pressure CVD, a catalyst method is used to partly convert hydrogen into hydrogen radicals. Proper examples of the catalyst include 3d-transition metals such as platinum, palladium, reduced nickel, cobalt, titanium, vanadium, and tantalum; compounds of metals such as aluminum, nickel, platinum-silicon, platinum-chlorine, platinum-rhenium, nickel-molybdenum, and cobalt-molybdenum; and mixtures or compounds of any of the above transition metals and alumina or silica gel. In addition, Raney catalysts of cobalt, ruthenium, palladium, nickel, and the like, and mixtures or compounds of any of those Raney catalysts and carbon can be used. These catalysts are used in a granulated, reticular, or powder state. Materials having a low melting point and markedly increasing the initial absorption rate of a reactive substance, and materials containing alkali metals such as sodium which easily vaporize are not suitable for the catalyst. Examples of such unfavorable materials are copper and tungsten. Experiments revealed considerable degradation of the catalyst at a temperature higher than the decomposition temperature of a reactive substance. The amount and the density of the catalyst depend on the effective contact area with a reactive gas, and may be adjusted when necessary. Active hydrogen radicals are generated by passing hydrogen through the catalyst being heated. Active ozone is generated by passing oxygen through an ozonizer.
In forming a SiOx film by using an atmospheric pressure CVD apparatus in which a substrate is heated, organic silane such as ethyl orthosilicate in a tank is bubbled with a carrier gas such as nitrogen. Oxygen is introduced into the apparatus while being partly converted into ozone in passing through the ozonizer. Hydrogen is introduced into the apparatus through the catalyst.
Where nitrogen oxide is added to a SiOx film, organic silane in a tank is bubbled with a carrier gas such as a carrier gas of nitrogen oxide (NxOy) such as NO, NO2 or N2O. Oxygen is introduced into the apparatus while being partly converted into ozone in passing through the ozonizer. Hydrogen is introduced into the apparatus through the catalyst.
All gases are supplied to the substrate in a mixed state from a gas nozzle having a dispersing mechanism. In forming a film by atmospheric pressure CVD by using only ethyl orthosilicate and ozone, an oxide film is formed much differently depending on whether the surface of a substrate is hydrophilic or hydrophobic. While a normal film can be formed on a substrate having a hydrophobic surface, abnormal film formation or reduction in film forming rate likely occurs with a hydrophilic surface. There occurs problems when an oxide film is formed on at least part of a hydrophilic surface. In contrast, the invention, which is associated with the use of hydrogen radicals, can not only provide the impurity blocking effect but also prevent abnormal film formation and reduction in film forming rate because active hydrogen terminates the substrate surface to thereby create a hydrophobic surface. In particular, these effects are remarkable when hydrogen is introduced by an amount 0.1 to 1 times the amount of a carrier gas such as nitrogen. Where ethyl orthosilicate is directly gasified by heating it, these effects are enhanced by a factor of 1 to 5.
Where nitrogen oxide is added to a SiOx film, nitrogen oxide can be used as a carrier gas. Similar effects can be obtained by using, as a carrier gas, nitrogen or the like rather than nitrogen oxide and introducing nitrogen oxide by a separate system.
Although in the above description hydrogen radicals are generated by plasma in plasma CVD and by a catalyst method in atmospheric pressure CVD, they may be generated in opposite manners. That is, active hydrogen radicals may be generated in advance by a catalyst method and then introduced into a plasma CVD apparatus. It is also possible to generate active hydrogen radicals in advance by discharging and then mix those with other gases by a gas nozzle of an atmospheric pressure CVD apparatus.
Where an oxide film is formed by using an organic silane type source gas, an oxygen source gas is used because active oxygen radicals, oxygen ions, and ozone are necessarily used. In the invention, H2O may be used to additionally use active hydrogen radicals or hydrogen ions. However, since H2O and an organic silane source gas react with each other very actively, there is a possibility that a pipe may be clogged if they are mixed with each other in the pipe before their reaction on a substrate. It is preferable that in a plasma CVD apparatus the pipes for introducing an organic silane source gas and H2O are separately provided.